In motor vehicles with internal combustion engines which operate with charging, for example, by means of an exhaust gas turbocharger, during acceleration, mainly in full load accelerations from low rotational speed, very high deviations from a setpoint charging pressure occur because an existing actual charging pressure concurs with the previous, lower rotational speed, but the setpoint charging pressure for acceleration is (under certain circumstances significantly) higher. Adjustment and/or control of the charging pressure attempts to equalize the actual charging pressure to the setpoint charging pressure as quickly as possible by the pressure setting device for setting the turbine inlet pressure being set accordingly. For example, guide vanes of variable turbine geometry of the exhaust gas turbocharger can be closed; this leads to acceleration of the turbine and of the compressor driven by it, whereupon the actual charging pressure rises. Setting the pressure setting device results in a major increase of turbine inlet pressure, whereby the medium pressure of charge alteration of the internal combustion engine also rises. But at the same time, among other things due to the mass inertia of the turbine and the compressor, only a comparatively moderately higher intake manifold pressure is available for increasing the amount of air in the cylinder. The intake manifold pressure therefore rises more slowly than the turbine inlet pressure. Since the turbine inlet pressure essentially corresponds to the pressure downstream from the internal combustion engine, the internal combustion engine must counteract this when exhaust gases are expelled. Since during acceleration the turbine inlet pressure rises quickly, but the intake manifold pressure, however, comparatively slowly, the efficiency of the internal combustion engine drops. Thus, on the crankshaft of the internal combustion engine, against the wishes of the driver of the motor vehicle for maximum acceleration, the maximum torque of the internal combustion engine is not available.
DE 195 31 871 C1 discloses a method for setting the charging pressure in an internal combustion engine charged by means of an exhaust gas turbocharger with an adjustable turbine guide apparatus. The charging pressure is to be set to a given charging pressure setpoint which is dependent on the operating point. For this purpose, a pressure difference is determined which is computed from the turbine inlet pressure and the intake manifold pressure. These pressures are measured by way of sensors and the measured values are supplied to a control unit. Furthermore, the measured values of the rotational speed of the internal combustion engine and the current injection amount are supplied to the control unit. This has the disadvantage that there must be a plurality of values as measured values, as a result of which the number of sensors is comparatively large. For example, a residual amount of gas also remains in a cylinder, i.e., the amount of gas remaining in the cylinder after an expulsion process is ignored.
On this basis, the object of the invention is to improve a method for controlling and/or adjusting the turbine inlet pressure of an exhaust gas turbocharger of an internal combustion engine of the initially mentioned type such that it manages with a minimum number of sensors and nevertheless accomplishes high efficiency of the internal combustion engine.